The use of pressure measurements in small confined spaces is important in a number of different fields. In the field of diagnostic medicine and monitoring of patients, it is often necessary or useful to measure relatively small pressure changes inside various organs in the individual's body. A number of different devices have been constructed to measure these pressure changes. Such devices include pressure sensing catheters that may be used in coronary arteries, devices for use in the urethra, and esophageal pressure sensing instruments.
One example of a need to detect an internal organ pressure change is esophageal pressure analysis. The ability to detect and display pressure differences over time provides a tool for manometric analysis both in the esophagus and potentially other parts of the gastrointestinal tract such as the stomach, duodenum, small bowel, colon, and anorectum.
Gastrointestinal motility disorders remain significant both in terms of the number of patients having symptoms of these disorders and the health care resources required to treat these disorders. Imaging methods (including endoscopy and radiography) provide some information regarding gastrointestinal organ structure and the movement of contents within these organs. Other imaging techniques are limited to diagnosis of disorders only if the disorder is characterized by a change to the organ's appearance or conspicuous abnormalities in the movement of the contents within such organs. However if the gastrointestinal disorder is simply an abnormality in the contracting function of the organ, an alternative diagnostic method is required. Manometry provides a sensitive measure of pressure change within an elongate organ, allowing additional useful information for diagnosis, treatment or monitoring of a disorder.
A number of different devices to measure pressure (specifically within human organs) have been disclosed. For example, U.S. Pat. No. 4,887,610 discloses a manometric catheter that includes a sleeve segment having two attached metal electrodes. This design allows the simultaneous measurement from a single location of pressure and electrical events specifically in human sphincters.
U.S. Pat. No. 4,873,990 discloses a probe for measuring circumferential pressures in a body cavity. This reference discloses the measurement of urodynamic pressure for evaluating human urinary sphincter function. Along the length of the probe are a number of deformable wall sensors. These wall sensors have flexible sidewall areas and a means to modulate the signal as the wall of the probe moves under the influence of external pressure.
U.S. Pat. No. 4,739,769 discloses a pressure transducer in which a fluid circulated through a tube at a constant flow rate expands into a bubble in a catheter. Absent an external pressure a bubble expands where there is no increase in the flow resistance to the system.
U.S. Pat. No. 5,987,995 discloses a fiberoptic pressure catheter including a light source, an optical fiber coupled to receive light from the light source and the sensor head that is optically coupled to the optical fiber. The housing has an opening that is enclosed by a membrane. The membrane may move in response to pressure differences between the membrane chamber and the pressure outside a sensor head. A resilient ribbon is coupled to the chamber such that it may move in front of the optical fiber. The ribbon is also coupled to the membrane such that it is repositioned by the membrane in response to pressure changes, thereby reflecting varying amounts of light back into the optical fiber based on the amount of pressure on the membrane.
U.S. Pat. No. 5,983,727 discloses a plurality of membranes including an incompressible mount and a deformable membrane mounted over the mount such that there is a cavity between said membrane and mount surface. A non-contact transducer within the mount detects deflection of the membrane.
U.S. Patent Application Ser. No. 60/343,714, also owned by the present applicant, discloses various methods and algorithms for visualization of values, including internal pressure measurement. Such visualization includes display in a number of formats of pressure readings.
All of the above references are hereby incorporated by reference for all purposes herein.
There are a number of limitations of the prior art. These include the inability to provide sufficient number of solid state sensors in a sufficiently small diameter tool to allow for a pressure sensor that is able to reliably resolve the spatial characteristics of pressure waves in elongate organs. The pressure sensing catheters currently available with a higher number of pressure sensors are of the water-perfused pneumohydraulic designs. These designs are not solid state, tend to be cumbersome and expensive, and are technically challenging to use. One drawback of such designs is that to overcome gravity effects, the patient must remain supine to ensure that the external transducers are at the level of the esophagus. In addition, sterilization of these catheters is difficult.
In addition, while a sufficient number of sensor sites has been achieved using perfussed water technology, these sensor sites have highly localized “spot” sensitivity and hence render unreliable measurements in regions of physiological asymmetry such as the pharynx and the upper esophageal sphincter. The use of circumferential sensing yields reliable measurements in these regions.
In addition providing a robust, easily sterilizable and simpler to manufacture device is needed.